The present disclosure relates to systems and methods that provide video and data over a cable transmission network.
Referring to FIG. 1, cable TV (CATV) systems were initially deployed as video delivery systems. In its most basic form the system received video signals at the cable head end, processed these for transmission and broadcast them to homes via a tree and branch coaxial cable network. In order to deliver multiple TV channels concurrently, early CATV systems assigned 6 MHz blocks of frequency to each channel and Frequency Division Multiplexed (FDM) the channels onto the coaxial cable RF signals. Amplifiers were inserted along the path as required to boost the signal and splitters and taps were deployed to enable the signals to reach the individual homes. Thus all homes received the same broadcast signals.
As the reach of the systems increased, the signal distortion and operational cost associated with long chains of amplifiers became problematic and segments of the coaxial cable were replaced with fiber optic cables to create a Hybrid Fiber Coax (HFC) network to deliver the RF broadcast content to the coaxial neighborhood transmission network. Optical nodes in the network acted as optical to electrical converters to provide the fiber-to-coax interfaces.
As the cable network evolved, broadcast digital video signals were added to the multiplexed channels. The existing 6 MHz spacing for channels was retained but with the evolving technology, each 6 MHz block could now contain multiple programs. Up to this point, each home received the same set of signals broadcast from the head end so that the amount of spectrum required was purely a function of the total channel count in the program line-up.
The next major phase in CATV evolution was the addition of high speed data service, which is an IP packet-based service, but appears on the HFC network as another 6 MHz channel block (or given data service growth, more likely as multiple 6 MHz blocks). These blocks use FDM to share the spectrum along with video services. Unlike broadcast video, each IP stream is unique. Thus the amount of spectrum required for data services is a function of the number of data users and the amount of content they are downloading. With the rise of the Internet video, this spectrum is growing at 50% compound annual growth rate and putting significant pressure on the available bandwidth. Unlike broadcast video, data services require a two-way connection. Thus, the cable plant had to provide a functional return path. Pressure on the available bandwidth has been further increased with the advent of narrowcast video services such as video-on-demand (VOD), which changes the broadcast video model as users can select an individual program to watch and use VCR-like controls to start, stop, and fast-forward. In this case, as with data service, each user requires an individual program stream.
Thus, the HFC network is currently delivering a mix of broadcast video, narrowcast video, and high speed data services. Additional bandwidth is needed both for new high definition broadcast channels and for the narrowcast video and data services. The original HFC network has been successfully updated to deliver new services, but the pressure of HD and narrowcast requires further change. The HFC network is naturally split into the serving areas served from the individual fiber nodes. The broadcast content needs to be delivered to all fiber nodes, but the narrowcast services need only be delivered to the fiber node serving the specific user. Thus, there is a need to deliver different service sets to each fiber node and also to reduce the number of subscribers served from each node (i.e. to subdivide existing serving areas and thus increase the amount of narrowcast bandwidth available per user).
FIG. 1 is a generalized representation of part of the cable TV infrastructure, which includes the cable head end; the Hybrid Fiber Coax (HFC) transmission network, and the home. The CATV head end receives incoming data and video signals from various sources (e.g., fiber optic links, CDN's, DBS satellites, local stations, etc.). The video signals are processed (reformatting, encryption, advertising insertion etc.) and packaged to create the program line up for local distribution. This set of video programs is combined with data services and other system management signals and prepared for transmission over the HFC to the home. All information (video, data, and management) is delivered from the head end over the HFC network to the home as RF signals. In the current practice, systems in the head end process the signals, modulate them to create independent RF signals, combine these into a single broadband multiplex, and transmit this multiplex to the home. The signals (different video channels and one or more data and management channels) are transmitted concurrently over the plant at different FDM frequencies. In the home, a cable receiver decodes the incoming signal and routes it to TV sets or computers as required.
Cable receivers, including those integrated into set-top boxes and other such devices, typically receive this information from the head end via coaxial transmission cables. The RF signal that is delivered can simultaneously provide a wide variety of content, e.g. high speed data service and up to several hundred television channels, together with ancillary data such as programming guide information, ticker feeds, score guides, etc. Through the cable receiver's output connection to the home network, the content is delivered to television sets, computers, and other devices. The head end will typically deliver CATV content to many thousands of individual households, each equipped with a compatible receiver.
Cable receivers are broadly available in many different hardware configurations. For example, an external cable receiver is often configured as a small box having one port connectable to a wall outlet delivering an RF signal, and one or more other ports connectable to appliances such as computers, televisions, and wireless routers or other network connections (e.g., 10/100/1,000 Mbps Ethernet). Other cable receivers are configured as circuit cards that may be inserted internally in a computer to similarly receive the signals from an RF wall outlet and deliver those signals to a computer, a television, or a network, etc. Still other cable receivers may be integrated into set-top boxes, such as the Motorola DCX3400 HD/DVR, M-Card Set-Top, which receives an input signal via an RF cable, decodes the RF signal to separate it into distinct channels or frequency bands providing individual content, and provides such content to a television or other audio or audiovisual device in a manner that permits users to each select among available content using the set top box.
As previously mentioned, the CATV transmission architecture has been modified to permit data to flow in both directions, i.e. data may flow not only from the head end to the viewer, but also from the viewer to the head end. To achieve this functionality, cable operators dedicate one spectrum of frequencies to deliver forward path signals from the head end to the viewer, and another (typically much smaller) spectrum of frequencies to deliver return path signals from the viewer to the head end. The components in the cable network have been modified so that they are capable of separating the forward path signals from the return path signals, and separately amplifying the signals from each respective direction in their associated frequency range.
The Hybrid/Fiber Coax (HFC) cable network architecture broadly depicted in FIG. 1 includes a head end system 10 having multiple devices for delivery of video and data services including EdgeQAMS (EQAMs) for video, cable modem termination systems (CMTS) for data, and other processing devices for control and management. These systems are connected to multiple fiber optic cables 12 that go to various neighborhood locations that each serve a smaller community. A fiber optic neighborhood or multi-neighborhood node 14 is located between each fiber optic cable 12 and a corresponding trunk cable 16, which in turn is interconnected to the homes 20 through drop cables 18 and feeder cables (not shown). Because the trunk cable 16, as well as the branch networks and feeder cables 18, each propagate RF signals using coaxial cable, the nodes 14 convert the optical signals to electrical signals that can be transmitted through a coaxial medium, i.e. copper wire. Similarly, when electrical signals from the home reach the node 14 over the coaxial medium, those signals are converted to optical signals and transmitted across the fiber optic cables 12 back to the systems at the head end 10. The trunk cables 16 and/or feeder cables 18 may include amplifiers 17. Connected to each trunk cable 16 is a branch network that connects to feeder cables (or taps) that each enter individual homes to connect to a respective cable receiver.
Hybrid fiber/coax networks generally have a bandwidth of approximately 750 MHz or more. Each television channel or other distinct content item transmitted along the forward path from the head end to a user may be assigned a separate frequency band, which as noted earlier has a typical spectral width of 6 MHz. Similarly, distinct content delivered along the return path from a user to the head end may similarly be assigned a separate frequency band, such as one having a spectral width of 6.4 MHz. In North America, the hybrid fiber/coax networks assign the frequency spectrum between 5 MHz and 42 MHz to propagate signals along the return path, and assign the frequency spectrum between 50 MHz and 750 MHz or more to propagate signals along the forward path.
Referring to FIG. 2, a cable modem termination system (CMTS) 30 may be installed at the head end, which instructs each of the cable modems when to transmit return path signals, such as Internet protocol (IP) based signals, and which frequency bands to use for return path transmissions. The CMTS 30 demodulates the return path signals, translates them back into (IP) packets, and redirects them to a central switch 32. The central switch 32 redirects the IP packets to an IP router 34 for transmission across the Internet 36, and to the CMTS which modulates forward path signals for transmission across the hybrid fiber coax cables to the user's cable modem. The central switch 32 also sends information to, and receives information from, information servers 38 such as video servers. The central switch 32 also sends information to, and receives information from, a telephone switch 40 which is interconnected to the telephone network 42. In general, cable modems are designed to only receive from, and send signals to, the CMTS 30, and may not communicate directly with other cable modems networked through the head end.
FIG. 3 shows an exemplary architecture for delivering CATV content between a head end 10 to a node 14. The head end 10 may in some instances include a plurality of direct modulation EdgeQAM units 50 which each receive digitally encoded video signals, audio signals, and/or IP signals, and each directly outputs a spectrum of amplitude-modulated analog signal at a defined frequency or set of frequencies to an RF combining network 52, which in turn combines the received signals. An optical transmitter 54 then sends the entire spectrum of the multiplexed signals as an analog transmission through an optical fiber network 56 along a forward path to the node 14. The fiber optic network, as will be explained in more detail later, is also capable of conveying optical signals from the node 14 to the head end 10 via an optical path between a transmitter 58 in the node 14 and a receiver 60 in the head end. In the specification, the drawings, and the claims, the terms “forward path” and “downstream” may be interchangeably used to refer to a path from a head end to a node, a node to an end-user, or a head end to an end user. Conversely, the terms “return path”, “reverse path” and “upstream” may be interchangeably used to refer to a path from an end user to a node, a node to a head end, or an end user to a head end. Also, it should be understood that, unless stated otherwise, the term “head end” will also encompass a “hub,” which is a smaller signal generation unit downstream from a head end, often used for community access channel insertion and other purposes, that generally mimics the functionality of a head end, but may typically not include equipment such as satellite dishes and telephone units. Hubs are commonly known to those skilled in the art of the present disclosure. It should be understood that although FIG. 3 illustrates a head end 10 that utilizes direct modulation EdgeQAMs, other architectures may employ other modulators, such as an analog EdgeQAM modulator or a Converged Cable Access Platform (CCAP) modulation system.
Directly-modulated EdgeQAM units have become increasingly sophisticated, offering successively higher densities, which in turn means that each EdgeQAM unit can process more channels of CATV data. For example, modern EdgeQAM modulation products can now simultaneously generate 32 or more channels on a single output port. With more channels being modulated per output port, the amount of combining required by the RF combining network 52 is reduced, with a corresponding simplification in the circuitry at the head end. The term ‘QAM’ is often used to interchangeably represent either: (1) a single channel typically 6 MHz wide that is Quadrature Amplitude Modulated (thus a “32 QAM system” is shorthand for a system with 32 Quadrature Amplitude Modulated channels; or (2) the depth of modulation used by the Quadrature Amplitude Modulation on a particular channel, e.g. 256 QAM means the signal is modulated to carry 8 bits per symbol while 4096 QAM means the signal is modulated to carry 12 bits per symbol. A higher QAM channel count or a higher QAM modulation means that a higher number of content “channels” can be delivered over a transmission network at a given standard of quality for audio, video, data, etc. QAM channels are constructed to be 6 MHz in bandwidth in North America, to be compatible with legacy analog TV channels and other existing CATV signals. However, more than one video program or cable modem system data stream may be digitally encoded within a single QAM channel. The term channel is unfortunately often used interchangeably, even though a QAM channel and a video program are not often the same entity—multiple video programs can be and usually are encoded within a single 6 MHz QAM channel. In this case, the modern EdgeQAM modulation products generate multiple instances of the 6 MHz bandwidth QAM channels. This simplifies the head end structure since some subset of the RF combining is now performed within the EdgeQAM units rather than in the external RF combining network. Packaging multiple QAM generators within a single package also offers some economic value.
As noted previously, modern CATV delivery systems over an HFC network provides content that requires communication along both a forward path and a return path, and over time, the quantity and quality of data transmission along each of these paths has increased drastically, which can be seen for example in the evolution of the DOCSIS standard from its original 1.0 release to the impending 3.1 release.
DOCSIS (Data Over Cable Service Interface Specifications) was developed by a consortium of companies, including Cable Labs, ARRIS, Cisco, Motorola, Netgear, and Texas Instruments, among others. The first specification, version 1.x, was initially released in March 1997 and called for a downstream throughput of approximately 43 Mbps and an upstream throughput of approximately 10 Mbps along a minimum of one channel. DOCSIS 2.0, released in late 2001 increased the maximum upstream throughput to approximately 31 Mbps, again for a minimum of one channel. DOCSIS 3.0, released in 2006 required that hardware be able to support the DOCSIS 2.0 throughput standards of 43 Mbps and 31 Mbps, respectively, along minimum of four channels in each direction. The DOCSIS 3.1 platform is aiming to support capacities of at least 10 Gbps downstream and 1 Gbps upstream using 4096 QAM. The new specification aims to replace the 6 MHz downstream and 6.4 MHz upstream wide channel spacing with smaller 25 kHz to 50 kHz orthogonal frequency division multiplexing (OFDM) subcarriers, which can be bonded inside a block spectrum that could end up being about 192 MHz wide for downstream and 96 MHz for upstream.
Providing increasing throughput along the upstream path has been particularly problematical the presence of upstream impairments including ingress. Ingress is radio frequency (RF) energy that has varying bandwidth and RF levels and can enter the CATV upstream plant via cable network defects. CATV network defects may include loose or corroded connectors, unterminated ports, and damaged cables, for example. Thus, to continue to meet the evolving needs of delivering CATV content, improved techniques for transmission along the upstream path, and particularly in the presence of upstream impairments. are desirable.